Materials
Acetonitrile (ACN) was purchased from Concord Technology Co. Ltd (Tianjin, China). Distilled water was produced by Milli-Q ultra-pure water system (Millipore, Billeria, USA).
Study population and sample collection
Access to human samples complied with both Chinese laws and the guidelines of the Tianjin Union Medical Center Ethics Committee, and written informed consent was obtained from the patients. 24 blood samples were collected from CRC patients undergoing colorectal resection and that were maintained under fasting conditions in the Department of Colorectal Surgery, the Tianjin Union Medical Center. These patients came from different places in China and had different social environments, dietary practices, and personal habits. The diagnosis of CRC was confirmed in all cases by histopathologic examination and immunohistochemistry. The preoperative blood samples were drawn at 7:00 o’clock on the second day before hospitalization, and the postoperative blood samples were drawn in 3d after surgery. During 3 h after surgery, the patients were not given any blood transfusion or other transfusion (electrolytes, glucose). Meanwhile, 24 blood samples were also collected from heath volunteers. Eight volunteers with anal benign diseases were selected for anal surgery, and specimens of benign anal disease lesions were selected, including hemorrhoids without infection and edema, and normal tissues near the anal fistula. Exclusion criteria were: (1) pregnant of lactating female; (2) metabolic diseases, such as diabetes mellitus (DM), gout, hyperlipidemia (HL); (3) hematopathy, including all types of leukemia and anemia; (4) any symptom of acute diseases during the last 2 weeks, such as: febrile, cough, headache, nausea, vomit, stomachache, diarrhea, hematuria; (5) momentous stress reaction during the last 2 weeks, such as psychic trauma and a large area of empyrosis; (6) use of specific drugs during the last 3 weeks, such as antibiotics (penicillins, quinolones, torlamician), hormone (deoxycortisone, dexamethasone), nonsteroid anti-inflammatory drugs (NSAIDs: acenterine, fragrans, saridon, contac), among others;(7)Excluding acute perianal diseases, such as perianal abscess, incarcerated hemorrhoids, etc. All the information about these CRC patients and were summarized in Table 1.
Sample preparation
The blood samples were kept in room temperature for 30 min, subsequently centrifuged at 3,000 rpm for 10 min at 4℃, the serum samples were stored at -80℃ until use. Plasma and colorectum tissue samples were thawed on ice. 200 μL of ACN were added to the 200 μL plasma then vortex-mixed for 1 minute. After centrifugation (12000 r/min, 5 min), the supernatant was taken for UPLC-Q-TOF-MS analysis. 30-50 mg of tissue sample was accurately weighted on ice. To extract all the ingredients, the tissue samples were fixed in 1 mL pure water and grinded in a mortar. 300 μL of ACN were added into 200 μL of the grinding fluid then vortex-mixed for 1 minute, centrifuged (12000 r/min, 5 min) and finally took the supernatant for UPLC-Q-TOF-MS analysis.
UPLC-Q-TOF-MS analysis
A Waters AcquityTM UPLC system (Waters, Milford, MA, USA), including a quaternary pump, an autosampler and a temperature controller, that was used for analyzing the prepared plasma and tissue samples. The chromatographic separation was performed on an ACQUITY UPLC BEHC18 column (100×2.1 mm, I.D., 1.8 μm) purchased from Waters at a flow rate of 0.3 mL/min and 5 μL injection volume. The run time was 13 min for each sample. The target column temperature and target sample temperature were maintained at 45 ℃ and 5 ℃, respectively. Water was used as solvent A and ACN was used as solvent B to conduct the gradient elution. 1% B for the first 0.5 min, 1%-50% B from 0.5 to 2 min, 50%-100% B from 2 to 9 min, 100%-1% B from 9 to 11 min and finally held for two minutes to get ready for the next injection. The column eluent was directed to the mass spectrometry without spilting.
Mass analysis was carried out on a XevoG2 Q-TOF (Waters MS Technologies, Manchester, UK) with ESI source both in positive and negative mode. The desolvation gas rate was set at 800 L/h at a temperature of 450 ℃, the cone gas rate was set at 50 L/h and the source temperature at 120 ℃.The capillary voltage and the cone voltage were set at 3000 V and 40 V in the positive ionization mode, and 2000 V and 40 V in the negative ionization mode, respectively. All analyses used the lockspray to ensure accuracy and reproducibility; the leucine encephalin was used as the lock mass (m/z 556.6306 for positive ion mode; m/z 554.6147 for negative ion mode). Data was collected in centroid mode from m/z 50 to m/z 1000 with a lockspray frequency of 15 s, and data averaging over ten scans.
Statistical analysis
PCA analysis was first used to detect the grouping trend and outliers. OPLS-DA analysis was performed to understand the difference between the two selected groups. Furthermore, variable importance in the projection (VIP) was calculated in OPLS-DA model to screen the potential biomarkers. Compounds whose VIP value was more than 1.5 in negative ion mode and 5.5 in positive ion mode that was considered as potential metabolic biomarkers in tissue samples, whose VIP value was more than 1.5 in negative ion mode and 8.0 in positive ion mode that was considered as potential metabolic biomarkers in plasma samples as well. Besides, the Wilcoxon test was conducted to determine the significance of each metabolite using IBM SPSS Statistics 20 then Graphpad Prism 6 was used to map the data. All univariate tests were two-sided and the significant differences between two groups to be compared were based on the paired test (*P<0.05, **P<0.01, ***P<0.001, ****P<0.0001).
Screening and analysis of biomarkers of CRC
The potential metabolic biomarkers were identified by the database of human metabolome database (HMDB, http://www.hmdb.ca/) and mapped into their biochemical pathways through metabolic enrichment and pathway analysis was based on database search Kyoto Encyclopedia of Genes and Genomes (KEGG, http://www.genome.jp/kegg/) and MetaboAnalysis 4.0 software.